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BONDS IN LIQUIDS & SOLIDS
INDEX INTRODUCTION METALLIC BONDS IONIC SOLIDS NETWORK SOLIDS DIPOLE–DIPOLE FORCES VAN DER WAALS FORCES HYDROGEN BONDS
INTRODUCTION In the solid or liquid phase molecules are very close to each other. We have already studied intramolecular bonds in molecules now, we will examine intermolecular forces of attraction in liquids and solids.
METALLIC BONDS Metals are solid at room temperature except for mercury. The attraction forces between metal atoms are strong. The valence electrons of metal atoms can easily move from the free orbitals of one atom to another and form an “electron sea”.
Attraction force between the negatively charged “sea of electrons” and the positively charged nuclei holds atoms together. This is called the metallic bond. In a group, metallic bond strength generally decreases from up to down. In a period, strength generally increases from left to right.
Metals are good conductors of heat and electricity Metals can be drawn into wires and hammered into shape easily.
Metallic bond is better maan!
The metallic bonding in Al is the strongest, and the weakest in Na.
IONIC SOLIDS When metal and nonmetal atoms come together, they form ionic bonds Electrostatic attraction occurs between the positive and negative charges holding the ions together. Metal ions are surrounded by nonmetal ions and nonmetal ions surrounded by metal ions.
. Ionic solids do not have a molecular structure. The melting and boiling points of ionic solids are very high Aqueous solution and molten state conduct electricity. Don’t conduct electricity Brittle, not ductile and can not be drawn into wires or hammered into plates. Very stable
NETWORK SOLIDS In some covalent substances, known as network solids, atoms are bonded together in a way that forms a network structure.
Diamond Each carbon atom is covalently bonded to four other carbon atoms forming a tetrahedral shape. The hardest natural substance. The bonds are formed by sp3-sp3 hybrid overlap.
Silicon carbide SiC is another network solid. Silicon carbide is used as an abrasive because of its hard structure.
Diamond and silicon carbide are nonconductors of electricity and have very high melting points.
Graphite Each carbon atom is bonded to three other carbon atoms with an angle of 120° between the bonds. The bonding involves sp2 – sp2 hybrid overlap. Because of weak bonding between the layers, the layers can slide over each other. Conduct electricity.
DIPOLE–DIPOLE FORCES The atrractions of the positive and negative poles of the molecules are called dipole–dipole forces. H2O ,HCl , NH3, H2S , PH3 , SO2 are samples. Dipole - dipole force is much weaker than the covalent bond within the molecule.
Dipole- Dipole Interactions d+ d-
Dipole- Dipole Interactions
VAN DER WAALS FORCES The intermolecular forces between nonpolar molecules in the liquid and solid state. By movement of electrons, nonpolar molecules becomes temporarily polar. The momentarily polar molecule makes polar its neighboring molecule. Thus a weak attraction occurs between the molecules.
Increasing number of atoms in a molecule increases the van der Waals attractive force. Van der Waals forces are stronger between molecules with high molecular masses. For small molecules, the van der Waals force is weaker than dipole - dipole forces and hydrogen bonding.
Formation of van der Waals forces. Molecules approaching each other gain a momentarily polar character.
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HYDROGEN BONDS An extra strong dipole-dipole attraction that occurs between molecules in which hydrogen is covalently bonded to the electronegative elements N, O and F.
Hydrogen bonds between water molecules are stronger than dipole-dipole and van der Waals forces.
Hydrogen bonds HF>H2O>NH3 HF H2O NH3
Because of hydrogen bonding the boiling points of HF,H2O and NH3 are greater than expected.
Ionic bond here Ionic bond covalent bond metallic bond hydrogen bond James bond He! He ! He! absent
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